Dupahar Me Pregnancy Test Kaise Kare: Pregnancy tests detect the presence of human chorionic gonadotropin (hCG), a hormone produced after a fertilized egg attaches to the uterine lining. The concentration of hCG increases rapidly in early pregnancy, doubling every 48 to 72 hours. Most tests are designed to detect hCG levels as low as 25 mIU/mL, but the accuracy depends on several factors, including the time of day.